‘Continuous sea-level rise is something we cannot avoid …’
By Summit Voice
FRISCO — Sea level rise is here to stay, according to researchers with the Potsdam Institute for Climate Impact Research, who recently published a study combining evidence from early Earth’s climate history with comprehensive computer simulations using physical models of all four major contributors to long-term global sea-level rise.
The results show a slow but inexorable rise — less than six feet by the end of this century — but the rate will increase as melting Antarctic and Greenland ice become bigger factors. Based on the Earth’s climate history, the long-term outlook is pretty clear. When CO2 levels were comparable to current values, the Earth was much warmer and sea levels were much higher.
The greenhouse gases that have already accumulated in the atmosphere will cause sea level to rise for centuries to come. Each degree of global warming is likely to raise sea level by more than 2 meters in the long-term, according to the study, published recently in the Proceedings of the National Academy of Sciences.
For now, thermal expansion of the ocean and melting mountain glaciers are still the most important factors causing sea-level change. But the Greenland and Antarctic ice sheets will be the dominant contributors within the next two millennia, according to the study. Half of that rise might come from ice-loss in Antarctica which is currently contributing less than 10 percent to global sea-level rise.
“CO2 emitted by burning fossil fuels, stays an awful long time in the atmosphere,” said Anders Levermann, lead author of the study. “Consequently, the warming it causes also persists.”
The oceans and ice sheets are slow in responding, simply because of their enormous mass, which is why observed sea-level rise is now measured in millimeters per year,” Levermann explained.
“The problem is: once heated out of balance, they simply don’t stop,” he said. “We’re confident that our estimate is robust because of the combination of physics and data that we use.”
“The Antarctic computer simulations were able to simulate the past five million years of ice history, and the other two ice models were directly calibrated against observational data – which in combination makes the scientists confident that these models are correctly estimating the future evolution of long-term sea-level rise,” said Peter Clark, a paleo-climatologist at Oregon State University and co-author on the study.
If global mean temperature rises by 4 degrees compared to pre-industrial times, which in a business-as-usual scenario is projected to happen within less than a century, the Antarctic ice sheet will contribute about 50 percent of sea-level rise over the next two millennia.
Greenland will add another 25 percent to the total sea-level rise, while the thermal expansion of the oceans’ water, currently the largest component of sea-level rise, will contribute about 20 percent. The contribution from mountain glaciers will decline to less than 5 percent, mostly because many of them will shrink to a minimum.
“Continuous sea-level rise is something we cannot avoid unless global temperatures go down again,” Levermann concluded. “Thus we can be absolutely certain that we need to adapt. Sea-level rise might be slow on time scales on which we elect governments, but it is inevitable and therefore highly relevant for almost everything we build along our coastlines, for many generations to come.”